linux-kernel - [PATCH 4.14 073/104] x86/kvm: Allow runtime control of L1D flush

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Date:   Tue, 14 Aug 2018 19:17:27 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Jiri Kosina <jkosina@...e.cz>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: [PATCH 4.14 073/104] x86/kvm: Allow runtime control of L1D flush

4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Thomas Gleixner <tglx@...utronix.de>

commit 895ae47f9918833c3a880fbccd41e0692b37e7d9 upstream

All mitigation modes can be switched at run time with a static key now:

 - Use sysfs_streq() instead of strcmp() to handle the trailing new line
   from sysfs writes correctly.
 - Make the static key management handle multiple invocations properly.
 - Set the module parameter file to RW

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Jiri Kosina <jkosina@...e.cz>
Reviewed-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@...hat.com>
Link: https://lkml.kernel.org/r/20180713142322.954525119@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kernel/cpu/bugs.c |    2 +-
 arch/x86/kvm/vmx.c         |   13 ++++++++-----
 2 files changed, 9 insertions(+), 6 deletions(-)

--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -639,7 +639,7 @@ void x86_spec_ctrl_setup_ap(void)
 #define pr_fmt(fmt)	"L1TF: " fmt
 
 #if IS_ENABLED(CONFIG_KVM_INTEL)
-enum vmx_l1d_flush_state l1tf_vmx_mitigation __ro_after_init = VMENTER_L1D_FLUSH_AUTO;
+enum vmx_l1d_flush_state l1tf_vmx_mitigation = VMENTER_L1D_FLUSH_AUTO;
 EXPORT_SYMBOL_GPL(l1tf_vmx_mitigation);
 #endif
 
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -237,12 +237,15 @@ static int vmx_setup_l1d_flush(enum vmx_
 
 	l1tf_vmx_mitigation = l1tf;
 
-	if (l1tf == VMENTER_L1D_FLUSH_NEVER)
-		return 0;
+	if (l1tf != VMENTER_L1D_FLUSH_NEVER)
+		static_branch_enable(&vmx_l1d_should_flush);
+	else
+		static_branch_disable(&vmx_l1d_should_flush);
 
-	static_branch_enable(&vmx_l1d_should_flush);
 	if (l1tf == VMENTER_L1D_FLUSH_ALWAYS)
 		static_branch_enable(&vmx_l1d_flush_always);
+	else
+		static_branch_disable(&vmx_l1d_flush_always);
 	return 0;
 }
 
@@ -252,7 +255,7 @@ static int vmentry_l1d_flush_parse(const
 
 	if (s) {
 		for (i = 0; i < ARRAY_SIZE(vmentry_l1d_param); i++) {
-			if (!strcmp(s, vmentry_l1d_param[i].option))
+			if (sysfs_streq(s, vmentry_l1d_param[i].option))
 				return vmentry_l1d_param[i].cmd;
 		}
 	}
@@ -296,7 +299,7 @@ static const struct kernel_param_ops vme
 	.set = vmentry_l1d_flush_set,
 	.get = vmentry_l1d_flush_get,
 };
-module_param_cb(vmentry_l1d_flush, &vmentry_l1d_flush_ops, NULL, S_IRUGO);
+module_param_cb(vmentry_l1d_flush, &vmentry_l1d_flush_ops, NULL, 0644);
 
 #define NR_AUTOLOAD_MSRS 8